Identification of activity peaks in time-tagged data with a scan-statistics driven clustering method and its application to gamma-ray data samples

The investigation of activity periods in time-tagged data-samples is a topic of large interest. Among Astrophysical samples, gamma-ray sources are widely studied, due to the huge quasi-continuum data set available today from the FERMI-LAT and AGILE-GRID gamma-ray telescopes. To reveal flaring episodes of a given gamma-ray source, researchers make use of binned light-curves. This method suffers several drawbacks: the results depends on time-binning, the identification of activity periods is difficult for bins with low signal to noise ratio. I developed a general temporal-unbinned method to identify flaring periods in time-tagged data and discriminate statistically-significant flares: I propose an event clustering method in one-dimension to identify flaring episodes, and Scan-statistics to evaluate the flare significance within the whole data sample. This is a photometric algorithm. The comparison of the photometric results (e.g., photometric flux, gamma-ray spatial distribution) for the identified peaks with the standard likelihood analysis for the same period is mandatory to establish if source-confusion is spoiling results. The procedure can be applied to reveal flares in any time-tagged data sample. The study of the gamma ray activity of 3C 454.3 and of the fast variability of the Crab Nebula are shown as examples. The result of the proposed method is similar to a photometric light curve, but peaks are resolved, they are statistically significant within the whole period of investigation, and peak detection capability does not suffer time-binning related issues. The method can be applied for gamma-ray sources of known celestial position. Furthermore the method can be used when it is necessary to assess the statistical significance within the whole period of investigation of a flare from an unknown gamma-ray source.Comment: 17 pages, 10 figures Accepted for publication in A&

Waiting times between gamma-ray flares of Flat Spectrum Radio Quasars, and constraints on emission processes

The physical scenario responsible for gamma-ray flaring activity and its location for Flat Spectrum Radio Quasars is still debated. The study of the statistical distribution of waiting-times between flares (the time intervals between consecutive activity peaks) can give information on the distribution of flaring times, and constrain the physical mechanism responsible for gamma-ray emission. We adopt here a Scan-Statistic driven clustering method (iSRS) to recognize flaring states within the FERMI-LAT data, and identify the time of activity-peaks. Results: Flares waiting times can be described with a poissonian process, consisting of a set of overlapping bursts of flares, with an average burst duration of about 0.6 year, and average rate of 1.3/y . For waiting times below 1d host-frame we found a statistically-relevant second population, the fast-component, mainly from CTA 102 data. The period of conspicuous detection of the fast component for CTA 102 coincides with the crossing-time of the superluminal K1 feature with the C1 stationary feature in radio reported in Jorstad et al. (2017); Casadio et al. (2019). Conclusions: To reconcile the mechanism proposed in Jorstad et al. (2017); Casadio et al. (2019) with the bursting-activity, we have to assume that plasma streams with a typical length of about 2pc (in the stream reference-frame) reach the recollimation-shock. Otherwise, the distribution of waiting-times can be interpreted as originating from relativistic-plasma moving along the jet for a deprojected length of about 30-50pc (assuming a Lorentz-factor=10), that sporadically produces gamma-ray flares. In magnetic-reconnection scenario, reconnection events or plasma injection to the reconnection-sites should be intermittent. Individual plasmoids can be resolved in a few favourable cases only (Christie et al., 2019); they could be responsible for the fast component.Comment: 15 pages, 11 figures, 3 tables, accepted for publication on Astronomy and astrophysic

ATel 7783: Optical/UV, High Energy Gamma-ray activity from the FSRQ PKS 1502+106

We asked a Swift ToO campaign on the FSRQ PKS 1502+106 (z=1.83853), triggered by prolonged High Energy activity detected with FERMI-LAT. The HE trigger detected activity at E > 10 GeV with TS ~153, from 2015-06-17 to 2015-07-10, following the prescription of Pacciani et al

ATel 8323: Optical, X-, Gamma-ray flare of the FSRQ PKS 2320-035

We asked a Swift ToO campaign on the FSRQ PKS 2320-035 (z=1.411), triggered by prolonged High Energy activity detected with FERMI-LAT. The trigger method detected activity at E > 20GeV/(1+z) with TS ~44 and emission up to 54 GeV from 2015-09-03 to 2015-11-16, following the prescription of Pacciani et al. 2014, ApJ, 790, 45. The flux integrated on the whole period is (32.1+-1.6)E^-8 ph cm^-2 s^-1 (E > 0.1 GeV), and the gamma-ray photon index 2.20+-0.06

SAFEE TE pseudo ESA TM packets

Si descrive il formato telemetrico dei dati prodotti dal test equipment della SAFE

ATel 8483: Optical, X, Gamma-ray activity of the FSRQ PKS 1313-333

We asked a Swift ToO campaign on the FSRQ PKS 1313-333 (z=1.21), triggered by prolonged High Energy activity detected with FERMI-LAT. The trigger method detected activity at E > 20GeV/(1+z) with TS ~79 from 2015-12-10 to 2015-12-30, following the prescription of Pacciani et al. 2014, ApJ, 790, 45. FERMI-LAT detected Two Gamma-ray photons of about 50 GeV within the last week

ATel 7588: Optical, X-, Gamma-ray flare of the FSRQ PKS 2032+107

We detected a gamma-ray flare from the FSRQ PKS 2032+107 (z=0.601), triggering on FERMI-LAT data at E > 10 GeV with TS ~46, from 2015-05-23 to 2015-06-02, following the prescription of Pacciani et al

ATel 9009: Optical, X, HE gamma-ray flare of the FSRQ S4 1030+61

The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed unusually high activity above 10 GeV from a source positionally consistent with the flat spectrum radio quasar S4 1030+61 (z=1.40)

ATel 7402: Optical, X-, Gamma-ray flare of the FSRQ PKS 1441+25

We detected a gamma-ray flare from the FSRQ PKS 1441+25 (z=0.939), triggering on FERMI-LAT data at E > 10 GeV with TS ~44, from 2015-03-21 to 2015-04-15, following the prescription of Pacciani et al

ATel 7526: Swift simultaneous observations of the VHE flare of S3 1227+25

We detected a gamma-ray flare from the low-synchrotron-peaked BL Lac (z=0.135) S3 1227+25, triggering on FERMI-LAT data at E > 10 GeV with TS ~35, from 2015-05-06 to 2015-05-15, following the prescription of Pacciani et al. ..